1. Field of the Invention
The present invention relates to a multi-channel communication method for wireless local area network (WLAN) devices with a single radio interface. More particularly, the present invention relates to a multi-channel media access control (MAC) method for WLAN devices with a single radio interface.
2. Description of the Related Art
For the past decade the Institute for Electrical and Electronics Engineers (IEEE) 802.11 standards have provided interoperability among WLAN devices. IEEE 802.11 has also succeeded in implementing timely amendments to the standard (for example, 802.11a, 802.11g, 802.11e, 802.11i, and 802.11n) addressing the different needs that become evident with time. Presently, 802.11s is being developed to define wireless mesh links between WLAN devices.
An important part of the IEEE WLAN standards have been addressing the link between an access point (AP) and its stations (STAs). A prevalent topology for networking between APs and STAs is a basic service set (BSS) network where a set of STAs is controlled by a single coordinator, the AP. A system used to interconnect a set of APs and the integrated local area network (LAN) is called the distribution system (DS). The DS is primarily a wired network. An important objective of 802.11s is to specify functionality that will allow access points (APs) to communicate wirelessly with each other (thereby extending the current wired distribution system (DS) and form a wireless distribution system (WDS)) as well as allow 802.11s nodes to relay traffic on behalf of each other (multi-hop communication).
FIG. 1 schematically illustrates WLAN mesh network components.
In contrast to an STA in a BSS network, the basic unit in a 802.11s mesh network, as shown in FIG. 1, is a mesh point (MP) 100. MPs can relay frames on behalf of other MPs, hop-by-hop, as a router does in wired networks. It can also be seen from FIG. 1 that WLAN mesh network also provides wireless links among APs referred to as mesh access points (MAPs) 110. As the wireless links do not require wired infrastructure, and the goal is to configure these devices in an unmanaged fashion, the expectation is that deployment of WLAN mesh networks can be accomplished promptly to cover a wide service range.
While MAC-layer routing and management framework for mesh networks are also key components of the WLAN mesh network, the present invention focuses on the MAC related aspects dealing with the multi-channel operation. A WLAN access control scheme defines a mechanism in which at least two MPs can communicate with each other in one channel. The multi-channel operation based on the single radio interface is an access scheme using one channel. Specifically, a channel to be commonly used between all devices is referred to as a “common channel.”
When the common channel has changed to a different channel for multi-channel operation in MPs with a single radio interface, the common channel state can be no longer detected. In other words, an MP cannot communicate with an arbitrary MP on the common channel. Although a sender MP selects the data channel to be used for data transmission by exchanging Request to Send (RTS) and Clear to Send (CTS) frames with a recipient MP on common channel, the sender MP cannot listen to RTS and CTS frames on other channels. Moreover, as RTS and CTS frames are devised to address the hidden-node problem, such an MP may destroy on-going data transmissions after switching the channel.